Device for applying a force to the underframe of a railway vehicle, for the inclination of the underframe or the transverse stabilization of the vehicle

ABSTRACT

A device for applying a tilting force on the body of a railway vehicle comprises elements for detecting and calculating the force to be applied, and hydraulic cylinder-piston devices (12, 12&#39;) having a reversible action from the energy point of view by taking or reconstituting energy from or to at least one hydraulic accumulator (26). Hydraulic cylinder devices (12, 12&#39;) are fed by two motor-pumps (70, 72) interconnected mechanically by a shaft (74), one motor-pump having hydraulic inlets and outlets connected, with a high pressure accumulator (26) and a low pressure feeder (28), respectively, and the other motor-pump having inlets and outlets connected with the chambers of the cylinder-piston devices. One of the two motor-pumps (70, 72) has a variable capacity, the variation in the capacity being controlled by the elements for detecting and calculating the force to be applied.

This application relates to copending U.S. patent application Ser. No.07/613,646, filed Dec. 20, 1990, now allowed in the names of the sameinventors.

BACKGROUND OF THE INVENTION

The present invention relates to railway vehicles and more particularlyto a device adapted to apply on the body of the vehicle a force fortilting the body about a longitudinal axis, or a force compensating forthe centrifugal and centripetal forces acting on the vehicle in a curve,of the type comprising at least one force-applying hydraulic cylinderdevice and elements for detecting and calculating the force to beapplied.

It will be recalled that the tilt of the vehicle body about an axiswhich is longitudinal or parallel to the track is a means employed oncertain passenger railway vehicles for reducing the discomfort of thepassengers resulting from the fact that the vehicle travels through thecurves at a speed which is higher--and sometimes lower--than theequilibrium speed corresponding to the natural cant of the track.Depending on whether the vehicles travel through the curve above orbelow the equilibrium speed, the passengers are exposed to accelerationswhich are, relative to the floor of the car, respectively centrifugal orcentripetal, this being all the more true because cars which have nobody tilting equipment and a conventional suspension in a low bearingplane, tilt in the wrong direction (they lean toward the exterior of thecurve when the speed is higher than the equilibrium speed and leantoward the interior of the curve in the opposite case).

Disregarding the passive systems whose suspension plane is higher thanthe center of gravity of the body and whose performances are poor owingto the inertias involved and to the relatively weak return action of theforces of gravity, a certain number of studies, and even constructions,exist which are based on active devices whose purpose is to return thebody to a set position more rapidly than the aforementioned passivesystems.

To the set position corresponds an apparent gravity force (resultingfrom the gravity force of the earth and the centrifugal accelerationforce due to the curve) whose component parallel to the floor of the caris, in certain cases, nil and, in other cases, has a limited value; tominimize the effect on the passenger of transverse accelerationsparallel to the floor of the vehicle, that constitutes a spatialreference for the passenger placed inside the vehicle.

The commercial interest of the body tilt is to improve the comfort ofthe passenger for given speeds in curves or, for a given comfort,increase the speed in the curves.

BRIEF SUMMARY OF THE INVENTION

The present invention has in particular as an object to provide acontribution to the systems of the active type which may be classifiedin two categories which are the following:

1st category: the body tilt is achieved by means of mechanical partsconnecting two solid parts of the vehicle, the sole purpose of which isto ensure the degree of freedom of rotation about the longitudinal axis:it concerns pins and bearings or an assembly of links. The motion ofrelative rotation between the two aforementioned solid parts is obtainedby these mechanical parts and the required energy is supplied throughcylinder devices placed between the two solid parts in question. Thistype is the most widely used and is for example illustrated by theGerman document DE-A-2 001 282 or British document GB-A-2 079 701;

2nd category: the body tilt is achieved without the necessity tomaterialize the axis of rotation by means of machined mechanical parts.It is sufficient to compress the suspension, usually the secondarysuspension, on one side of the vehicle and to allow it to extend on theother side, the energy to be supplied for causing the movement beingtransmitted, as before, through cylinder devices, but this time thecylinder devices are placed in parallel with the suspension. Thiscategory is illustrated for example by the French document FR-A-2 231550 or German document DE-A-2 156 613.

The invention is applicable to the two aforementioned categories evenif, for reasons of simplification, the figures and commentaries whichfollow refer exclusively to the tilt systems of the second category.

The invention also concerns a phenomenon accompanying the increase inspeed on sinuous lines which must be taken into account jointly with thebody tilt when higher speeds are in fact desired to be employed on suchlines. What is found and is well known, derives from the fact that inincreasing the speed in a given curve, the transverse forces transmittedto the track ineluctably vary as the square of the speed. Apart from theforces on the track itself, the rolling stock takes up all the playsavailable transversely which results in a deterioration of the comfort,as will be explained.

The plays involved have essentially two sources: the play of the axlesin the rail and the play between the abutments of the secondarysuspension. The primary suspension is itself designed to have a certainstiffness conditioned by the stability and, as it usually does not haveabutments, is not harmful.

The taking up of the plays in a curve on the axles is caused by a badoperation of the axles; consequently the front axle of each truck copiesthe defects on the inner rounded portion of the outer rail of the curve.It is advisable under these conditions to conform to the constructionalprescriptions set forth in the patent application PCT/FR 89/00310 filedon Jun. 19, 1989, which corresponds to U.S. patent application Ser. No.07/613,860, filed Dec. 17, 1990, now abandoned.

As concerns the conventional secondary suspensions, i.e. the passivesuspensions, they are based on the principle of high flexibility,moreover both vertically and transversely, so as to filter the defectsof the track. But the filtering no longer occurs for the geographicalaccidents. Thus, in a curve, the secondary suspension bottoms in anunpleasant manner at the moment of entering the curve, and this is allthe more so with a more flexible secondary transverse suspension and,furthermore, owing to the planing of the outer rail by the flange of thewheels. The bottoming, even against an elastic abutment, is the cause ofa transmission to the interior of the body of unpleasant vibrationsthroughout the time during which the curve is travelled through.

The remedy for this problem is known: it consists in applying on thebody of the vehicle a force opposed to the centrifugal force exerted onthe body during passages through a curve. Thus, for example, in respectof a body suspended conventionally by means of passive suspensions,there must be applied to the body during passages through the curves asystem of forces equivalent to a centripetal force substantiallyparallel to the plane of the track at the place at which the vehicle islocated, applied at the center of gravity of the body and substantiallyequal to the centrifugal force thus exerted on the body minus thecentripetal component due to the natural cant of the track.

The determination of the system of forces to be applied to the body ofthe vehicle is not part of the present invention.

The invention has the further object, within the framework of a deviceof the type mentioned at the beginning of this specification, to improvethe performances of such devices by means of a special arrangement.

More precisely, according to the invention, the force-applying elementis a hydraulic element having a reversible action from the energy pointof view by taking off or restoring the energy from or to at least onehydraulic accumulator. Such an arrangement permits, for obtaining thedesired result, employing only a minimum amount of energy owing to therecuperation of energy.

An arrangement of this type has been described in the patent applicationPCT/FR 89/00266 filed on May 31, 1989, which corresponds to U.S. patentapplication Ser. No. 07/613,646, filed Dec. 20, 1990; the content ofwhich is incorporated in the present application by reference. In thisapplication, the principle of recuperation of energy is employed fordamping the oscillatory motions of the railway vehicle, whereas,according to the present invention, this principle is employed for thebody tilt or the transverse compensation of the centrifugal force.

In an advantageous arrangement of the invention, the double-actinghydraulic cylinder device for applying the force is fed from one of themotor-pumps of a group of two motor-pumps whose shafts areinterconnected and whose inlets and outlets are connected, for one, witha high pressure accumulator and a low pressure feeder and, for theother, with the two chambers of the cylinder device.

One of the two motor-pumps has a variable capacity, the variation in thecapacity being controlled by the elements for detecting and calculatingthe force to be applied.

According to a less advantageous arrangement, since it operates on anon-off principle, the signal leaving the processing circuit can be sentto a driving element having three positions controlling through the samemechanical shaft, three directional control valves which open hydrauliccircuits to the double-acting cylinder device or the two double-actingcylinder devices. The hydraulic connections are, on one hand, to a highpressure oil reservoir--also termed hydraulic accumulator--and, on theother hand, to a low pressure oil feeder connected to the atmosphere.The reserve of high pressure oil is possibly reconstituted by means of apump controlled by a pressure controller so as to maintain a constantpressure in the accumulator. The connection is achieved by twodirectional control valves as a function of the direction of the signaldelivered by the processing circuit so as to bring about the desiredmotions of rotation or transverse motion when the cylinder device orcylinder devices must accelerate the motion of the body in one directionor the other. When, on the contrary, the speed of rotation of the bodyis suitable, or when the body is subjected to no significant force onthe part of the transverse cylinder device, i.e. if the signal deliveredby the processing circuit is lower than a fixed threshold, the cylinderdevice or cylinder devices are isolated from the accumulator and fromthe feeder and connected as a by-pass by a third direction controlvalve.

The transverse stabilization or the stabilization in rotation about thelongitudinal axis of a railway body may be achieved jointly with asystem for damping the vertical motion according to the device describedin the aforementioned patent application PCT/FR 89/00266 (U.S. patentapplication Ser. No. 07/613,646). This permits the pooling of a certainnumber of elements conditioned by the two or three stabilizations andwill be described in more detail hereinafter.

But still more generally, the invention may be integrated into a systemin which both the vertical motions and the horizontal motions are eachthe object of a stabilization and therefore of a damping.

According to another characteristic of the invention, it may be ofinterest, when it is made to contribute in a tilting system of theaforementioned second category, to neutralize, when this is possible,the energies involved in the compression and decompression of thesprings, or at least, to minimize them so as to reduce the capacity ofthe hydraulic accumulator. This is possible for the pneumaticsuspension. For this it is sufficient to put the cushions incommunication through a large-section pipe and a valve which will beopened each time the pressure difference between the two cushionsexceeds a predetermined threshold, but any other criterion announcing alarge motion of orientation will be capable of likewise serving tocontrol the opening of the aforementioned valve.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will be apparentfrom the following description, with reference to the accompanyingdrawings wherein:

FIG. 1 is a schematic cross-sectional view of a body of railway rollingstock, showing the implantation of the tilt stabilization cylinderdevices;

FIG. 2 is a diagrammatic view of operation of the tilt control;

FIG. 3 is a view similar to FIG. 2 of operation of a stablization of abody tilted about the longitudinal axis combined with a verticalstabilization;

FIG. 4 is a view similar to FIG. 1 showing the implantation of a lateralbody stabilization cylinder device; and

FIG. 5 is a diagrammatic view of a lateral control operation structure.

DETAILED DESCRIPTION

Returning to FIG. 1, there are shown in cross-section the conventionalcomponents of a body tilt, i.e. a body 2 of railway rolling stockbearing on a truck frame 4 through a secondary suspension 6. The truckframe is itself supported, through a primary suspension not shown, bymeans of wheels 8 which roll along rails 10. Tilt hydraulic cylinderdevices 12 are engaged between the body 2 and the truck frame 4 andcause a rotation about the longitudinal axis in accordance with ordersgiven by a servomechanism diagrammatically represented in FIG. 2 anditself receiving tilt information, for example from an accelerometer 40having a substantially transverse axis connected to the body anddisposed in the latter as close as possible to the longitudinal axis ofrotation; but the body tilt information may also be given by other knownmeans, such as memories of the line synchronized with the position ofthe vehicle on the line, etc.

When the accelerometric signal delivered by the accelerometer 40corresponds to a significant acceleration of the body in the directiontoward the right (for example in a right-hand curve), the cylinderdevice 12 placed on the right side of the body is compressed while theleft cylinder device 12 is extended so as to compensate for at least apart of the centrifugal force by the earth gravity component. Thesituation is the opposite when the transverse body acceleration itselfchanges direction.

Lastly, when the transverse body acceleration is below a minimumthreshold, no order is given to the tilt cylinder devices.

The principle of operation of the body tilt such as describedhereinbefore conforms to the prior art and is assumed to be known.Devices constructed in accordance with this principle may be improved,in the case where the secondary suspension is a pneumatic suspension, byinserting between the two pneumatic cushions 6 a differential valvehaving the reference numeral 6' in FIG. 1 so as to reduce the force tobe overcome for positioning the body in rotation about the longitudinalaxis. Of course, in this case the levelling valves associatedconventionally with the pneumatic cushions (the function of which is tomaintain a constant height of the cushions by pneumatic inflation ordeflation) must be at the same time neutralized.

In FIG. 2 there is shown diagrammatically the operation of the controlwhich is of conventional type. As an example, there has been consideredhere for tilting the body the signal delivered by an accelerometer 40which is thereafter inserted in a processing circuit 42 constituted by afilter 44 (according to test results, this filter could possibly beeliminated) followed by an amplifier 46 receiving conventionally apartfrom the accelerometric signal an anticipation signal 10. The latter maybe taken from an accelerometer placed in an ahead position in the sametrain so as to be re-entered, after the suitable time delay, into theamplifier-saturator 46.

The elements effecting the body tilt or the power elements of theservomechanism conform to one of the arrangements described in theaforementioned patent application PCT/FR 89/00266 (U.S. patentapplication Ser. No. 07/613,646) and comprise two hydraulic motor-pumps70 and 72 interconnected by a shaft 74 and hydraulically connected, oneto the high and low pressure reservoirs 26 and 28, and the other to thetwo chambers of the double-acting cylinder devices 12. One of the twomotor-pumps has a variable capacity and the latter is modified as afunction of the output of the processing circuit 42.

With reference to FIGS. 2, 5 and 3, the operational relationship betweenthe two separated hydraulic fluid circuits connected to motor pump 70and motor pump 72 respectively is not hydraulic buy mechanical. The twomotor pumps are linked by shaft 74.

The motor-pump 70 has a variable capacity which is controlled by theoutput signal delivered by the circuit 42 or 18.

Let us assume that the railway vehicle enters a curved portion of therailroad, e.g. a right curve. The corresponding lateral acceleration issensed by the accelerometer 40 and the circuit 42 or 18 delivers asignal modifying the capacity of the motor-pump 70 (said capacity wasnil before because the vehicle was on a straight line) so that themotor-pump 70 starts to rotate and the torque is transmitted through theshaft 74 to the motor-pump 72, which creates differential pressure inthe cylinder piston unit 12 or 12' on opposite sides of the piston toproduce relative displacement between the piston and cylinder whichcauses the body to tilt in a direction and up to an extent such that acomponent of the gravitational forces parallel to the floor compensatesthat of the centrifugal force due to the curve.

When leaving the curve, the accelerometer 40 delivers a signal which,through the control circuit, entails a reduction of capacity of themotor-pump 70, so that the rotation of shaft 74 is reversed as thedriving torque imposed on the motor-pump 72 due to the forces exerted bythe body on the cylinder-piston unit 12 or 12' is higher than thepotential torque of the motor-pump 70; this motor-pump 70 is thenpassive and causes oil from the lower-pressure reservoir BP 28 to returnto the high-pressure reservoir HP 26.

Depending on results of on-line tests, it can be decided whether it isdesirable to install an automatic pump 38 which, as a complement of thelateral pumping, ensures a constant pressure difference between the highand low pressure reservoirs.

It will be observed that the described system is an open-loopservocontrol system: there corresponds in a steady state (stationarystate) to a horizontal acceleration detected by the accelerometer avalue of the force applied by the cylinder devices 12 which, on one sideof the body compresses the secondary suspension and on the other siderelieves it. But it is possible, without departing from the scope of theinvention, to employ closed-loop servocontrols according to a knowntechnique. The criteria of compensation: total compensation, partialcompensation according to a fixed rate, compensation up to a ceiling,etc. are not part of the invention and are to be chosen according tocriteria of appropriate physiological comfort.

It will moreover be observed that the body motion is achieved by asystem taking off energy from its energy reserve or, on the contrary,regenerating it, at least partly, according to the phases of the motionand according to the same principle as that described in theaforementioned PCT patent application. The hydraulic pipes aredimensioned as large as possible so as to increase the energyregeneration to the maximum extent.

It will be noted lastly that the motion of rotation such as that justdescribed hardly interferes in the general vertical motion resultingfrom the body suspension. At the very most there is a certain braking ofthe vertical motions owing to pressure drops in the pipes. If thesebrakings are not sufficient to brake the vertical body motions,conventional dampers acting jointly with the cylinder devices should beadded. They are not shown in FIG. 1.

According to another characteristic of the invention, in body tiltingsystems constructed in accordance with the arrangement shown in FIG. 2,it is possible to return in the event of emergency to a suspension ofconventional type by the action of directional control valves 76 and 78.The latter are shown in FIG. 2 in the position where the body tiltingdevice is in normal operation. If a bad operation of the tilting systemis found by automatic detectors or by the personnel on board the vehicleor train, directional control valves 76 and 78 may be automatically ormanually shifted, as the case may be, through a quarter of a turn in theclockwise direction. The electric and hydraulic body tiltingservocontrol is then isolated from the cylinder devices 12. The latterthen behave as ordinary dampers in which the oil is throttled incalibrated tubes 80 which interconnect the directional control valves 76and 78.

FIG. 3 shows as an example how to achieve joint operation of a body tiltstabilization according to the characteristic of the present inventionand an overall vertical motion stabilization according to thearrangement disclosed in the aforementioned patent application PCT/FR89/00266 (U.S. patent application Ser. No. 07/613,646) now allowed.

A system controlling the vertical motion identical to that described inthis patent application produces a vertical motion correction signalwhich is sent through adders 56 and 58 to two power systems controllingthe lateral cylinder devices 12. This control system comprises anaccelerometer having a substantially vertical axis 14, possibly a filter20, then an integrator 22 and its discharge circuit 22 connected inparallel with an amplifier 21, then an amplifier 24 which produces thevertical body motion control signal.

Together with the control signal of the vertical motion of the whole ofthe body mentioned hereinbefore there is produced according to the samearrangements as those referred to in respect of FIG. 2, a body tiltcontrol signal. The latter is added or subtracted with the suitable signwith respect to the vertical motion control signal in these adders 56and 58. The signals issuing from these adders are then sent to twoactuating systems or power elements constituted by the same componentsas those described with reference to FIG. 2, except that each of thesystems feeds only a single cylinder device. The components of these twosystems, including the cylinder devices 12 they feed, carry the samereferences as in FIG. 2 to which the index "b" or the index "t" areadded, depending on whether they refer to a double-acting cylinderdevice placed on the starboard side or the port side of the body.

Reference is now made to FIGS. 4 and 5 for explaining the control devicefor the lateral stabilization according to another aspect of theinvention.

In FIG. 4 there is shown a body 2 resting on a truck frame 4 (possiblyon an axle for rolling stock having solely axles) through a secondarysuspension 6. The frame 4 bears (through possibly a primary suspensionnot shown) on wheels 8 which roll along rails 10. The body is stabilizedby a double-acting hydraulic cylinder device 12' exerting horizontal andtransverse forces between the body and the frame 4. The cylinder device12' is fed from a high pressure reservoir 26, the oil pass pressurebeing received in a low pressure reservoir 28.

The control of the lateral stabilization shown in FIG. 5 is effected bymeans of a signal delivered by an accelerometer 14 having asubstantially horizontal axis fixed to the body. The accelerometricsignal is processed in a processing circuit 18 comprising possibly afilter 20 (high-pass), an integrator 22 and a discharge circuit 22'connected in parallel with an amplifier 21. The resulting signalconstitutes for the circulation of the vehicle in a straight line thesignal controlling the transverse motions of the body. This signal needsto be completed in curves by a signal representing the centrifugal forceuncompensated by the natural cant of the track which assumessubstantially the following value when the body inclination is effectedin the manner indicated in FIGS. 4 and 5.

    M(V.sup.2 /R-gc/1500)

where M represents the fraction supported by the truck in question ofthe mean value of the mass of the body, V the travelling velocity of thevehicle, R the radius of the considered curve, c the value of the cantof the track expressed in millimeters (standard 1,500 mm wide track) andg the acceleration due to the gravity of the earth.

In the example taken from FIG. 5, the signal is obtained from atachometric and localizing central unit 38 delivering the elements ofvelocity and path followed through (C=1/R and c).

The correction signal (slow motion having a topographical evolution) iscalculated in the calculator 39 and added, with the suitable sign, tothe signal controlling the transverse body motions (rapid motions) atthe input of an amplifier 24.

The actuating system of the servomechanism, the subject matter of theinvention, comprises, by way of example, two motor-pumps 70 and 72mechanically interconnected by the shaft 74 and hydraulically connected,one with a high pressure accumulator 26 and a low pressure feeder 28,the other with the two chambers of the cylinder device 12'. Further, oneof the motor-pumps has a variable capacity, the latter being controlledby the signal issuing from the amplifier 24.

Note finally that the invention may be applied to a vehicle where all ofthe vertical, horizontal and tilting about a longitudinal axis motionsare controlled by an active suspension of the type described herein formerely the transverse motions.

We claim:
 1. In a device for applying a compensating force on a bodysupported on a frame of a railway vehicle for compensating for otherforces on said body including at least one hydraulic cylinder-pistonmeans comprised of a piston operating in a cylinder, and detecting andcalculating means for detecting and calculating the force to be applied,the improvement comprising:at least one double acting hydrauliccylinder-piston means operatively connected between the frame and thebody; high pressure accumulator means mounted on the vehicle; lowpressure fluid feeder means mounted on the vehicle; two reversiblemotor-pump means mounted on the vehicle; shaft means operativelyconnecting said two motor-pump means so that rotation of either one ofsaid motor-pump means rotates the other of said motor-pump means; inletand outlet means for each of said motor-pump means; inlet and outletmeans for each of said accumulator and feeder means; two pressurechambers in said at least one hydraulic cylinder-piston means onopposite sides of said piston thereof; first fluid conduit means betweensaid outlet means of said accumulator means and one of said inlet andoutlet means of one of said motor-pump means; second fluid conduit meansbetween the other of said inlet and outlet means of said one of saidmotor-pump means and said inlet of said feeder means; third fluidconduit means between said outlet of said feeder means and said inlet ofsaid accumulator means for feeding hydraulic fluid from said feedermeans to said accumulator means; fourth fluid conduit means between oneof said inlet and outlet means of the other of said motor-pump means andone of said chambers; and fifth fluid flow conduit means between theother of said inlet and outlet means of said other of said motor-pumpmeans and the other of said chambers; one of said motor-pump meanshaving a variable capacity, the variation of said capacity beingcontrolled by said detecting and calculating means for detecting andcalculating the force to be applied, so that operation of one of saidmotor-pump means by said detecting and calculating means operates theother of said motor-pump means via said shaft means for operating saidat least one hydraulic cylinder-piston means for applying force to saidbody relative to said frame for compensating for said other forces onsaid body.
 2. The device as claimed in claim 1 wherein:said forceapplying device applied a tilting force about a longitudinal axis ofsaid body and said other forces are tilting forces; said at least onehydraulic cylinder-piston means comprises first and second double actinghydraulic cylinder-piston means; and further comprising sixth fluidconduit means between one of said chambers of said first cylinder-pistonmeans and one of said chamber of said second cylinder-piston means; andseventh fluid conduit means between the other of said chambers of saidfirst cylinder-piston means and the other of said chambers of saidsecond cylinder-piston means; said first and second cylinder-pistonmeans being connected between said frame and said body on opposite sidesof said vehicle so that said first and second cylinder-piston meansexert respective applied tilting forces on said body in oppositedirections.
 3. A device as claimed in claim 1, wherein said other forcesare tilting forces on said body tending to tilt said body about alongitudinal axis thereof and further comprising:pneumatic cushion meansbetween said frame and said body for providing a resistance to saidother tilting forces on said body relative to said frame; and saiddevice for applying said tilting force is controlled by said detectingand calculating means for at least partly neutralizing said resistanceof said cushion means in curves when said applied tilting producesexcessive forces on said cushion means.
 4. A device as claimed in claim2 and further comprising:pneumatic cushion means between said frame andsaid body for providing a resistance to said other tilting forces onsaid body relative to said frame; and said device for applying saidtilting force is controlled by said detecting and calculating means forat least partly neutralizing said resistance of said cushion means incurves when said applied tilting produces excessive forces on saidcushion means.
 5. A device as claimed in claim 3 wherein:said cushionmeans comprises two pneumatic cushion devices in spaced relationshipadjacent opposite sides of said vehicle; and differential valve meansare interposed between said two pneumatic cushion means, saiddifferential valve means being adapted for opening in response to apressure difference between said two cushions which exceeds apredetermined threshold pressure.
 6. A device as claimed in claim 4wherein:said cushion means comprises two pneumatic cushion devices inspaced relationship adjacent opposite sides of said vehicle; anddifferential valve means are interposed between said two pneumaticcushion means, said differential valve means being adapted for openingin response to a pressure difference between said two cushions whichexceeds a predetermined threshold pressure.
 7. A device as claimed inclaim 1 wherein:said other forces are centrifugal forces; and said atleast one hydraulic cylinder-piston means comprise double actinghydraulic cylinder-piston means mounted between said body and said framefor applying a transversal force to said body for compensating for saidcentrifugal forces.